Bought Second hand phone

[Al900]

I bought a second hand phone from someone who had took the phone out on contract in 2023 . It's iPhone 15 pro max. 
when I put my giff gaff sim card in it's saying at the top no service with a little p beside it wich means primary and under it it says giff gaff with a little s beside it rich means secondary.

is the phone locked to a network or is it blacklisted ? The seller is now not answering me after I bought it from them on Facebook Marketplace . I don't know how to upload a screenshot here 

[Al900]

 

[63johnw]

Hi @Al900  if the phone is originally from sky then it's not locked as all phones supplied by sky are unlocked. P is for primary and that's saying there is no service. S is for secondary and that's showing as your giff gaff sim. Are you trying to add a sky sim ?