How to Combine Multilple workbooks/tabs into one?

Hi and welcome to the forum.

The error message you get is generally caused by merged cells. Get rid of them. Most of us who use Excel for serious applications avoid them like the plague. They just cause problems too numerous to mention here. Often the format 'Center across selection' achieves the same thing without the hassle.

Do you mean you want to combine many WORKBOOK files into one tab, or many WORKSHEETS in the same workbook into one tab. And if the former just one sheet from each workbook or many?

Let us know and upload either a couple of sample workbooks or the workbook with the several sheets.

When you combine the information do you want to keep any formulae, or convert everything to values?

In the 4 workbooks there is nothing to identify the clients. If that is necessary data, it should be added to your data. Other than that, the data has the same 4 columns so, select the data and copy and paste the data into a new workbook. Copy each successive workbook under the previous one. If the data is out of order, sort on the date column.