Error with Power BI Custom Connector -cannot convert a value of type Function to type Text.

[jaime_blackwell]

Hi All,

I'm building a custom connector for Power BI that queries Xero's API. 

When used in Power BI the connector returns an error after successful authentication "We cannot convert a value of type Function to type Text."

When I test the connector in Visual Studio I get the error "Set is undefined" after successful authentication. 

Code for my connector is here: https://gist.github.com/jaimeblackwell/1e510ba24c4d71a0c5a6902e29e2da5b

I've tried wrapping my variables in functions such as Text.From() but the same error still occurs. Any assistance or feedback will be greatly appreciated!

[jaime_blackwell]

Hi Xiaoxin,

Thank you for that suggestion. I've added in Diagnostics.Trace into my Test Connection expression. However there is nothing appearing in the logs. The connector works perfectly with Power BI Desktop, just not Service or data gateway. Updated code is here:

https://gist.github.com/jaimeblackwell/1e510ba24c4d71a0c5a6902e29e2da5b#file-gistfile1-txt-L4

Have I configured Test Connection incorrectly or is it a problem with my Data Gateway?

Thank you!

[v-shex-msft]

Hi @jaime_blackwell,

If your data connector works well on the desktop side, I'd like to suggest you take a look at the flowing document about using a custom data connector with gateway and power bi service security. (power bi service has more limits on custom/development contents usage due to its security requirements)

Use custom data connectors with the on-premises data gateway 

Power BI Security#data-storage-security 
Regards,

Xiaoxin Sheng

[v-shex-msft]

HI @jaime_blackwell,

This seems like a common error notice, and it appears when you try to do type conversions or use M query functions with wrong data types.

In my opinion, I'd like to suggest you add some 'debug output' codes into your connector to output the logs to the debug panel and help you trace/locate the M query processing steps. (it should help us to find out which steps cause the issue)

Regards,

Xiaoxin Sheng