This error is not related to Eikon Data API, it's related to how Pandas library handle the input Excel file.
However, I spotted that the error is because the excel file contains the string '--' in column Coupon and when Pandas's read_excel function is executed, it's failed to convert the string into int hence the error is thrown.
According to this question on Stackoverflow, one of the ways to fix this is to convert the file from xlsx to csv, then use read_csv instead of read_excel to read the data
Hope this could help
An alternative way to pull down the contracts is to utilize the Search APIs directly as opposed to manually creating and exporting a spreadsheet and importing it into your application.