( Error: Can't subset columns that don't exist.) help please

would you please someone help me here I have been stuck in this code for days now and its driving me crazy

Error: Can't subset columns that don't exist.

x Column TotalNM_Cost doesn't exist.
Run rlang::last_error() to see where the error occurred.

however I have defined TotalNM_Cost so whats the problem ?
Your help is much appreciated. Iam trying to creat a matrix

Hi, welcome!

We don't really have enough info to help you out. Could you ask this with a minimal REPRoducible EXample (reprex)? A reprex makes it much easier for others to understand your issue and figure out how to help.

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Thank you I solved it it was my mistake . Thanks anyway