A71 dual sim does not send mms from sim 2

[Tunshill]

I have 2 sims in my a71 both with Giffgaff. Both have the same corrected Apn file. Sim 1 will send mms but sim 2 will not. Would I be right to assume that it is only possible to send mms from one of the sims. 

[Pugs1957]

Yes, your assumption is correct, only one sim is used for data.