Adding a new offer number

Could you attach a copy of your file? Explain in detail what you want to do using a few examples from your data and referring to specific cells, rows, columns and sheets. De-sensitize the data if necessary.

It's difficult to work with a picture. Perhaps you could upload a copy of your file to a free site such as www.box.com or www.dropbox.com. Once you do that, mark it for 'Sharing' and you will be given a link to the file that you can post here. It would be of great help of you could include a sheet that shows what the end result would look like.

Does this help?
See attached.
If you want to post an example -> Press Go advanced(bottom right) and then scroll down -> manage attachments

Try the attached file. I'm not sure if this is what you were looking for but maybe it could be a start to work on. When you click on column A, a calendar will pop up for you to choose a date. Don't enter anything in column B. Make a selection in columns C, D and E and the offer number in column B will be added automatically. Don't enter anything in cell B1 or delete it. Even though you can't see its contents, it holds the offer number and the macro uses this number to generate the next number. Please let me know how it works for you and if you want to make any changes.

If I understand your requirement right, this could be one way the get the next number.
Change all the A1 Cell references to the cell you want changed.

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If the initials of the person offering it is in Cell H1 (=DropDown List) and the invoice number is in Cell A1, this might also be a consideration.

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Mumps1 and dotchiejack

The "offer" file have the button that I would like to have
The "tomasszz" file have all the data that I need

If you combine these two solutions, it would be exactly what I need.
I would like to have a button, after which the window will pop out. I would like there to pop up the options of choice: merchant, customer and supplier, and date. After accepting the selected options, a new line would appear and be given a new number. The order of the columns is not very important, it would be even better if the first column was the offer number, followed by the date, initials, customer, supplier (with the supplier must be one or several different selections that will be visible in the cell) and the unique offer number [example: 458-CC-12-2018]

EDIT: of course it is required to add new customer or supplier to the base when a new one appears to company

You should post an example file or give us at least the column headers.

Try the attached file.

Something like this?
When you make a mistake you can change the offers.
You can choose different suppliers by making different choises in the combobox.

Try the attached file.