"Saya tidak bisa menolak."

Translation: I cannot refuse.

[RussJohn]

I thought me- verbs required an object. Why doesn't this sentence have one?

[FarizAlfar]

It can. Every word with prefix 'Me-' is transitive. It may have an object or not

[dgaeremie]

Why tidak bisa and not tidak?

[clbaft]

Tidak, the adverb, negates a verb (tidak mau = don't want, tidak suka = don't like etc). In this sentence the verb is bisa or 'can' in English. So tidak bisa = can not

[Jon.Orble]

You can certainly say “saya tidak menolak” (= “I didn’t refuse” or “I won’t refuse”) but using “bisa” (“can”, or “able to”) adds extra meaning. It’s really the same in English: “I won’t refuse” is different to “I can’t refuse”.

[clbaft]

Yes, thanks for clarifying. I meant the verb that tidak is negating in this sentence is 'can', but maybe I could have been clearer. Without bisa you can still negate menolak with tidak, but as you said it becomes 'did not refuse' rather than cannot