Not sure about what your book actually says but me/te/nous/vous can be used as both direct and indirect object pronouns.

Your sentence translates then to:

Il ne peut pas m’acheter.

Same for:

Il m’a acheté, il t’a acheté, il nous a acheté

there are many pronouns and it can definitely be confusing. Here are the categories you’re talking about:

• pronoms personnels sujets: je, tu, il/elle/on, nous, vous, ils/elles
• pronoms compléments directs: me, te, le/la, nous, vous, les
• pronoms compléments indirects: me, te, lui, nous, vous, leur
• pronoms y et en (other situations)
• pronoms toniques: moi, toi, lui/elle, nous, vous, eux/elles

So to translate He bought you/ me/ us, you can say: Il t’/m’/nous a acheté-e-s -> don’t forget to adjust the participe passé with the COD!

To know more about these different categories in grammar, here is an article for you: https://sweet-french-learning.com/glossaire-grammatical/