pay

1

I had to pay the taxi.
I had to pay for the taxi.

Use pay + person/amount/bill: ‘pay the driver’, ‘pay £20’, ‘pay the bill’.

Use pay for + thing/service: ‘pay for dinner’, ‘pay for the hotel room’, ‘pay for the taxi’.

2

You can pay with credit card almost everywhere.
You can pay with a credit card almost everywhere.
You can pay by credit card almost everywhere.

Both structures are correct. Use with a credit card or by credit card.

3

A lot of public-sector workers don’t get a good pay.
A lot of public-sector workers don’t get good pay.

Pay is an uncountable noun when it means the money received for doing a job: ‘good pay’, ‘low pay’.

See CREDIT CARD