How to pass calculated total to a payment field?

hi, i use to be able to map the swuare widget to take the value from a field like "invoice amount" or total but csnt seem to figure out how to map these fields so i can hsve s customer pay for their invoice through the form, can someone contact or help me with  this

Would you like to pass total calculated on a form to payment Square payment field? 

If so, here is our guide: How-to-Pass-a-Calculation-to-a-Payment-Field

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