A dropdown component [label="Type"] has an invalid value for "value". All selected values must be present in the choiceValues array, but value was and choiceValues was 117; 118. (APNX-1-4198-000)

a!localvariables(local!leadData: rule!PRO_qrtLead(leadId: 244).data,

local!credentiallingTypes: if(
a!isNullOrEmpty(
local!leadData['recordType!TRO Lead.fields.credentialingTypeLookupRefId]
),
{},
local!leadData['recordType!TRO Lead.fields.credentialingTypeLookupRefId]
),

a!dropdownField(
label: "Type",
choiceLabels: local!TRO Lookup.fields.label,
choiceValues: local!TRO Lookup.fields.lookupRefId,
placeholder: "---Select Credentialling Types---",
value: local!credentiallingTypes,
saveInto: local!credentiallingTypes
))

As the error message indicates, you can only a value in the "value" parameter that is also present in the choice values. This is the basic nature of all the Appian components having multiple options to choose from. 

a!dropdownField(
                label: "Select " & cons!TTP_CONFIG_DISPLAY_VALUES[3],
                labelPosition: "ABOVE",
                placeholder: "Select a Data",
                choiceLabels: local!client['recordType!{a3480fb1-15c0-4549-8121-7b4bfe485728}TTP Client.fields.{022666ad-2a5e-48b1-a87a-a30eee29b231}firstName'],
                choiceValues: local!client['recordType!{a3480fb1-15c0-4549-8121-7b4bfe485728}TTP Client.fields.{7cefb235-e416-4c2f-b471-dc52652e4b18}clientId'],
                value: if(
                  and(
                    a!isNotNullOrEmpty(
                      local!client['recordType!{a3480fb1-15c0-4549-8121-7b4bfe485728}TTP Client.fields.{7cefb235-e416-4c2f-b471-dc52652e4b18}clientId']
                    ),
                    contains(
                      local!client['recordType!{a3480fb1-15c0-4549-8121-7b4bfe485728}TTP Client.fields.{7cefb235-e416-4c2f-b471-dc52652e4b18}clientId'],
                      ri!request.clientId
                    )
                  ),
                  ri!request.clientId,
                  null()
                ),
                saveInto: {
                  a!save(ri!request.clientid, save!value),
                  a!save(ri!request.consumerid, null())
                },
                searchDisplay: "AUTO",
                
                required: true,
               
                validations: {}
              )

Check the above code

You can use index function instead of a!isnullOrEmpty

index(recordType!Department(name: "Engineering"), recordType!Department.fields.name, "")

link: docs.appian.com/.../fnc_array_index.html

As I already pointed out in your duplicate thread, the value must resolve to a non-array NULL when initially loading the dropdown as empty.