"He is paying."
The difference between "bezahlt" and "bezahle" is basically the same difference between "pays" and "pay" - it depends on the pronoun before the verb:
- ich bezahle
- er/sie/es/man bezahlt
ihr bezahlt (note: ihr is second person plural formal, du and Sie take different conjugations)
- he/she/it/one pays
- you pay
Also, "bezahle" and "bezahlt" are the imperative (giving someone an order)
- "Bezahle!" ("pay!" (used with someone you'd refer to as "du"), "Bezahl!" is also possible)
- "Bezahlt!" ("pay! (used with a group you'd refer to as "ihr")
Lastly, "bezahle" is the Konjunktiv I conjugation for ich and er/sie/es/man, but that form is pretty rare in modern spoken and written German, and I wouldn't worry about how to form/use it if you're still a beginner.
Er einkaufen should be accepted as an answer
Why do you think so?
einkaufen means "shop" or "shopping". It does not mean "pay".
When the subject is er, the verb form ends in -t, not in -en (e.g. er trinkt, er isst, er hat, er bezahlt).
Even if einkaufen were correct, it would be er kauft ein, with -t on the verb and with the separable prefix ein- at the end.
Can we write it as "Er biezäle"
i learned that the e becomes ie, and the a becomes ä .. when conjugated for the the third person singular?
That is not true for all verbs.
For example, sehen has er sieht but stehen has er steht. tragen has er trägt but sagen has er sagt.
So you have to learn for each verb whether the vowel changes or not; you can't predict it just by looking at the verb.
And even if the vowel changes, it would only be the stem vowel -- the last one. be- is a prefix and would never change its vowel anyway.
And finally, bezahlen has a -h- which you dropped; and the personal ending for third person singular is -t, not -e.