Why does leaving prev carrier's SIM in phone cause problems?

[snap-crackle]

Hi. Switched from Fido last month. Left SIM in phone, using eSIM for Public. Received porting texts within the timeframe, just paid for the new plan, etc. Data works, can receive calls, can't call out. Reset network settings, still can't. Had to remove physical SIM, reset network settings, restart phone, for everything to work.

Why? CS agents said "Public has to be the primary SIM for it to work". What makes a SIM the "primary"? Is the physical SIM always the primary? If that's the case, then using eSIM with Public means it can't be used as one of two carriers in a dual-SIM phone. Which makes no sense to me.

Any insight? Thanks

[softech]

@snap-crackle 

it is not. problem, it is just easier for most.

first, since you already replies the text from Fido and the Fido service was going to stopped , it is easier to manage by just disable or delete the Fido som from the sim manager 

However, for those who need to have 2 SIMs running together, yes, they can keep them one as Primary and one as Secondary (or Business or whatever label they assign).  However, to use dual SIMs,  they also and should spend some time and configure which sim to use forncoice, text and data instead of leave the phone to decide.  Many are not aware of it , and in the case of port, the old sim card really no longer needed)l, hence the best advise is to ask people to remove or disable the other one 

Also, even other sim is needed, if is usually better to set the other sim disable first and make sure the new sim works.  Once the new sim is confirmed working, people can then enable the other sim back and start twesking on the settings to their liking