I can receive incoming cellphone calls, but I cannot make an outgoing cellphone call on Macbook

I can receive calls in my MacBook (Retina, 12-inch, 2017),

but I cannot make a call using it.

Running Mojave 10.14.6

I select the number in Facetime or Contacts or Messages

to call and it fails time and again. I keep getting a failed

message with the option to "Try again".

But . . . I can answer incoming calls.

I've checked setting after setting.

Same network, both my iPhone7+ and my MacBook (Retina, 12-inch, 2017)

are signed into same Apple ID . . . whats my error?

Searched internet for how to do this: I seem to have all settings correct.

What setting(s) am I missing?

Thanks!