At One Time
Adverb
いっぺんに
一遍にいろんなことを言われても、分からないわ。
If you say a bunch of things at once I won’t understand.
Remember how you learned that 一遍 means "once?" Well if you add に and make it an adverb, it becomes at once.
This has the same reading you learned with 一遍 so you should be able to remember this too!