Radio Button

Narmada , If you can attach your code it would easy to understand the issue.

a!formLayout(
label: "Payment",
contents: {
a!radioButtonField(
label: "Payment Type",
labelPosition: "ADJACENT",
choiceLabels: {"Online", "Bank Challan"},
choiceValues: {"Online", "Bank Challan"},
value: ri!Pay_Type,
saveInto: ri!Pay_Type,
choiceLayout: "COMPACT",
validations: {}
),
a!sectionLayout(
label: "Passport Seva Challan",
contents: {
a!columnsLayout(
columns:{
a!columnLayout(
contents:{
a!textField(
label: "SBI CBS Screen No:",
labelPosition: "ADJACENT",
value: ri!ScreenNo,
saveInto: ri!ScreenNo,
refreshAfter: "UNFOCUS",
validations: {}
)
}
),
a!columnLayout(
contents:{
a!textField(
label: "Fee Type",
labelPosition: "ADJACENT",
value: ri!FeeType,
saveInto: ri!FeeType,
refreshAfter: "UNFOCUS",
validations: {}
)
}
)
}
),
a!textField(
label: "Challan Number",
labelPosition: "ADJACENT",
value: ri!ChallanNo,
saveInto: ri!ChallanNo,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Challan Expiry Date",
labelPosition: "ADJACENT",
value: ri!ChallanDate,
saveInto: ri!ChallanDate,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Passport Office",
labelPosition: "ADJACENT",
value: ri!PassportOffice,
saveInto: ri!PassportOffice,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Passport Service Type",
labelPosition: "ADJACENT",
value: ri!PassportServiceType,
saveInto: ri!PassportServiceType,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Applicant Name",
labelPosition: "ADJACENT",
value: ri!ApplicantName,
saveInto: ri!ApplicantName,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Contact Number",
labelPosition: "ADJACENT",
value: ri!PhoneNumber,
saveInto: ri!PhoneNumber,
refreshAfter: "UNFOCUS",
validations: {}
),
a!integerField(
label: "Amount",
labelPosition: "ADJACENT",
value: ri!Amount,
saveInto: ri!Amount,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Signature",
labelPosition: "ADJACENT",
value: ri!Sign,
saveInto: ri!Sign,
refreshAfter: "UNFOCUS",
validations: {}
),
a!paragraphField(
label: "Instructions",
labelPosition: "ADJACENT",
placeholder: "1)Payment after challange expiry date will be rejected by Bank
2)Deposit the application fee at nearest SBI branch after be least 3 hours from generating the challan",
value: ri!Instructions,
saveInto: ri!Instructions,
refreshAfter: "UNFOCUS",
requiredmessage: "",
readOnly: true,
height: "SHORT",
validations: {}
)
},
showwhen: true),
a!sectionLayout(
contents: {
a!radioButtonField(
label: "Card Type",
labelPosition: "ADJACENT",
choiceLabels: {"Master Card", "Visa","Paypal","American Express"},
choiceValues: {"Master Card", "Visa","Paypal","American Express"}
,
value: ri!CardType,
saveInto: ri!CardType,
showwhen: if(ri!Pay_Type<>null,"",null),
choiceLayout: "COMPACT",
validations: {}
),
a!textField(
label: "Name on card",
labelPosition: "ADJACENT",
value: ri!Name,
saveInto: ri!Name,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Card Number",
labelPosition: "ADJACENT",
value: ri!CardNumber,
saveInto: ri!CardNumber,
refreshAfter: "UNFOCUS",
validations: {}
),
a!dateField(
label: "Expiry Date",
labelPosition: "ADJACENT",
value: ri!Date,
saveInto: ri!Date,
validations: {}
),
a!textField(
label: "CVV",
labelPosition: "ADJACENT",
value:ri!CVV,
saveInto: ri!CVV,
refreshAfter: "UNFOCUS",
validations: {}
)
},
showwhen: {}
)
/*showWhen: isnull(*/
/*ri!Pay_Type.challan*/
/*),*/
/*Showwhen:ri!Pay_Type="BankChallan",*/


},

buttons: a!buttonLayout(
primaryButtons: {
a!buttonWidgetSubmit(
label: "Submit",
style: "PRIMARY"
)
}
)
)

a!formLayout(
label: "Payment",
contents: {
a!radioButtonField(
label: "Payment Type",
labelPosition: "ADJACENT",
choiceLabels: {"Online", "Bank Challan"},
choiceValues: {"Online", "Bank Challan"},
value: ri!Pay_Type,
saveInto: ri!Pay_Type,
choiceLayout: "COMPACT",
validations: {}
),
a!sectionLayout(
label: "Passport Seva Challan",
contents: {
a!columnsLayout(
columns:{
a!columnLayout(
contents:{
a!textField(
label: "SBI CBS Screen No:",
labelPosition: "ADJACENT",
value: ri!ScreenNo,
saveInto: ri!ScreenNo,
refreshAfter: "UNFOCUS",
validations: {}
)
}
),
a!columnLayout(
contents:{
a!textField(
label: "Fee Type",
labelPosition: "ADJACENT",
value: ri!FeeType,
saveInto: ri!FeeType,
refreshAfter: "UNFOCUS",
validations: {}
)
}
)
}
),
a!textField(
label: "Challan Number",
labelPosition: "ADJACENT",
value: ri!ChallanNo,
saveInto: ri!ChallanNo,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Challan Expiry Date",
labelPosition: "ADJACENT",
value: ri!ChallanDate,
saveInto: ri!ChallanDate,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Passport Office",
labelPosition: "ADJACENT",
value: ri!PassportOffice,
saveInto: ri!PassportOffice,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Passport Service Type",
labelPosition: "ADJACENT",
value: ri!PassportServiceType,
saveInto: ri!PassportServiceType,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Applicant Name",
labelPosition: "ADJACENT",
value: ri!ApplicantName,
saveInto: ri!ApplicantName,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Contact Number",
labelPosition: "ADJACENT",
value: ri!PhoneNumber,
saveInto: ri!PhoneNumber,
refreshAfter: "UNFOCUS",
validations: {}
),
a!integerField(
label: "Amount",
labelPosition: "ADJACENT",
value: ri!Amount,
saveInto: ri!Amount,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Signature",
labelPosition: "ADJACENT",
value: ri!Sign,
saveInto: ri!Sign,
refreshAfter: "UNFOCUS",
validations: {}
),
a!paragraphField(
label: "Instructions",
labelPosition: "ADJACENT",
placeholder: "1)Payment after challange expiry date will be rejected by Bank
2)Deposit the application fee at nearest SBI branch after be least 3 hours from generating the challan",
value: ri!Instructions,
saveInto: ri!Instructions,
refreshAfter: "UNFOCUS",
requiredmessage: "",
readOnly: true,
height: "SHORT",
validations: {}
)
},
showwhen: true),
a!sectionLayout(
contents: {
a!radioButtonField(
label: "Card Type",
labelPosition: "ADJACENT",
choiceLabels: {"Master Card", "Visa","Paypal","American Express"},
choiceValues: {"Master Card", "Visa","Paypal","American Express"}
,
value: ri!CardType,
saveInto: ri!CardType,
showwhen: if(ri!Pay_Type<>null,"",null),
choiceLayout: "COMPACT",
validations: {}
),
a!textField(
label: "Name on card",
labelPosition: "ADJACENT",
value: ri!Name,
saveInto: ri!Name,
refreshAfter: "UNFOCUS",
validations: {}
),
a!textField(
label: "Card Number",
labelPosition: "ADJACENT",
value: ri!CardNumber,
saveInto: ri!CardNumber,
refreshAfter: "UNFOCUS",
validations: {}
),
a!dateField(
label: "Expiry Date",
labelPosition: "ADJACENT",
value: ri!Date,
saveInto: ri!Date,
validations: {}
),
a!textField(
label: "CVV",
labelPosition: "ADJACENT",
value:ri!CVV,
saveInto: ri!CVV,
refreshAfter: "UNFOCUS",
validations: {}
)
},
showwhen: {}
)
/*showWhen: isnull(*/
/*ri!Pay_Type.challan*/
/*),*/
/*Showwhen:ri!Pay_Type="BankChallan",*/


},

buttons: a!buttonLayout(
primaryButtons: {
a!buttonWidgetSubmit(
label: "Submit",
style: "PRIMARY"
)
}
)
)

I am assuming ri!Pay_Type is of type text. If its true, then just add the showWhen attribute with value as ri!Pay_Type="Bank Challan" in the sectionLayout(). I see in the commented part of the section you have "BankChallan" without any space.
Are you still getting the error you mentioned above? In the Card Type radio button field try changing the showWhen as not(isnull(ri!Pay_Type)) instead of if(). Hope it helps.