How can I fix shipping carrier issues in my new store?

Hello,

I am on the Basic Plan and do not have any issues on my 1st Store. On my new store I am having the following issues.

1 - I am attempting to fulfil orders and receive the attached message:

Fix errors to see shipping services

2 - I manually created packages and Priority Mail & UPS Express appear as options I do not see First Class Mail and receive the error message below when I try to create a label:

**USPS:**Shipping::Label id:689739006271 was unable to be associated with a carrier service

3 - Can POS support two stores on the app? If so, how?

Thank you in advance for your help