Dynamically send an SMS message

[LadyT]

Based on this table structure,

I want to create a bot that does the following:  When a new message is added in the Message table, the system will send an SMS message to the phone numbers where the Message category equals the PositionsHeld category

I have tried several conditions to dynamically populate the "To" field of the SMS message. My expression yields no errors. When I monitor the bot, the message I get says the "To" field is blank.

One example of an expression I used it below.

Select(PositionsHeld[v_SMS], ([Category] = [_THISROW].[Category]))

I have been at this for weeks and can't figure out why it's not working for me. Any assistance is very much appreciated. Thanks!!!