Matt:
I am already using PHP to help me with report writing but I don't transfer values from Retool to PHP as part of the process. It works on a MySQL data file that I prepare for it.
For example:
Suppose I have a customer who is over 30 days on a payment. I have that value (say 35) in the invoice file. If I could send that value to my PHP app it could decide what kind of reminder to prepare for the email.
I have tried to write this sort of logic in MySQL stored procedures and I have given up on that.