Both 嘛ma and 呗bei occur at the end of a statement implying that what is being said is obvious. 嘛ma expresses a sense of contradiction, whereas 呗bei conveys a tone of self-assertion:
Zhè hěn jiǎn dān ma！
(But) this is very simple. (How could you think otherwise?)
Zhè hěn jiǎn dān bei！
This is very simple. (You don’t need me to tell you that!)
Wǒ méi shēng tā de qì，tā shì wǒ péng yǒu ma ！
I wasn’t angry with her, she is my friend. (Despite what you/ others might think.)
I wasn’t angry with her. She is my friend. (Don’t you realize?)
Wǒ méi shēng tā de qì，tā shì wǒ péng yǒu bei！
Nǐ wéi shí me mǎi zhè me guì de xié ？
Why did you buy such expensive shoes?
Wǒ xǐ huān ma！
I like them. (Why shouldn’t I?)
Wǒ xǐ huān bei！
Because I like them. (That’s all./That’s that.)
 Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.