Run WebAPI Onload

Have you tried setting the integration as the value of a local variable, then using that local variable in the grid? 

https://docs.appian.com/suite/help/19.1/Grid_Tutorial.html#paging-and-sorting-configurations

For example, in the docs for the paging grid, (which you can find if you scroll slightly *up* from the anchor tag in the link above) they include an example of how to set value of a local variable called local!datasubset using the queryrecord() function. In the same way, you can set your datasubset variable for your paging grid (let's use the same local!datasubset variable name to be consistent) and specify your integration as its value. So, yours might be.  local!datasubset: rule!XYZ_MyWebApiIntegtation() 

Hello, I am facing a very similar issue. I try to trigger the integration on page load by assigning it to a local variable in the following fashion:

local!Trigger:a!refreshVariable(
  value:rule!TheIntegration(
    inputs:"inputs",
    onSuccess:{
      a!save(local!Result,a!fromJson(fv!result.Result))
    },
    onError:a!save(local!RTError,fv!error.message)
  ),
  refreshAlways: true
)

I do not get any errors but the result of calling the API is not stored anywhere. The variable local!Trigger will have the value "Smart Service" but I am getting no result or error. Note that I had to include "a!refreshVariable()" so that I did't get an error message saying "... smart service functions cannot be used in a local variable unless "refreshAlways" is true for that local variable using the a!refreshVariable() function."

Note: The API is tested and works perfectly on button click.

Hello, I am facing a very similar issue. I try to trigger the integration on page load by assigning it to a local variable in the following fashion:

local!Trigger:a!refreshVariable(
  value:rule!TheIntegration(
    inputs:"inputs",
    onSuccess:{
      a!save(local!Result,a!fromJson(fv!result.Result))
    },
    onError:a!save(local!RTError,fv!error.message)
  ),
  refreshAlways: true
)

I do not get any errors but the result of calling the API is not stored anywhere. The variable local!Trigger will have the value "Smart Service" but I am getting no result or error. Note that I had to include "a!refreshVariable()" so that I did't get an error message saying "... smart service functions cannot be used in a local variable unless "refreshAlways" is true for that local variable using the a!refreshVariable() function."

Note: The API is tested and works perfectly on button click.

Erik,

Your expression has onSuccess/onError with a!save() which means you are trying to modify data after calling the integration. On loading an expression/interface you will only be able to call integrations that query data, not the ones that modify data - see here:

https://docs.appian.com/suite/help/20.2/Call_an_Integration.html#call-an-integration-to-modify-data-in-an-interface-component-or-web-api

"Integrations that modify data are called like smart service functions using the rule! domain and can only be used in the saveInto parameter of a component or in a Web API."

Check hania's response above where the Integration object's Usage was changed from Modified Data to Queries Data. If you do that you can then get the result directly in your local!trigger variable.