{{msg-mw|Payflowpro gateway-error-msg-js|notext=1}}

That is how I translated it ("The following field is required:") . I am not certain that it is 100% correct, though.

I interpreted

• Payflowpro gateway-error-msg-js (page does not exist)

as the starting fragment of a sentence, that will be completed with

• Payflowpro gateway-error-msg-amount (page does not exist)
• Payflowpro gateway-error-msg-emailAdd (page does not exist)
• Payflowpro gateway-error-msg-fname (page does not exist)
• Payflowpro gateway-error-msg-lname (page does not exist)
• Payflowpro gateway-error-msg-street (page does not exist)
• Payflowpro gateway-error-msg-city (page does not exist)
• Payflowpro gateway-error-msg-state (page does not exist)
• Payflowpro gateway-error-msg-zip (page does not exist)
• Payflowpro gateway-error-msg-card num (page does not exist)
• Payflowpro gateway-error-msg-expiration (page does not exist)
• Payflowpro gateway-error-msg-cvv (page does not exist)

to make a full sentence, when the respective field is empty. But "The following field is required:" should also work, I believe.

That is currect - as stated in an earlier topic, IIRC. The code contains "payflowproGatewayErrorMsgJs + currField"

I've translated "The following field is required:" because in Galician "your" could be "o seu" or "a súa" depending on the noun which is next to it.

It would also have been possible to move the translation of "your" out of the first message and into each of the others.

Yep! Did precisely that.