Because the service is provided in Wisconsin - that transaction
is under THAT state jurisdiction and is regulated by Wisconsin state laws
The first step - to verify if the service provided is subject to sales tax.
Sales and use tax applies to sales of tangible personal property
, certain coins and stamps, certain leased property affixed to realty, certain digital goods, and specified services.
Specifically see following publication
page 33 where taxable services are listed.
If that service is taxable - you generally should pay sales tax.
If provided services are subject of sales tax - then...
Generally - you may only use exemption certificate if you purchase as a re=seller. In this case - you use an exemption certificate and do not pay sales tax to provider, but will charge sales tax from the purchaser and remit that amount to Wisconsin taxing authorities.
That is generally the purpose of the exemption certificate.
If these are taxable services which you purchase NOT to re-sell - you may not use an exemption certificate and must pay sales tax.
If provider doesn't charge sales tax - you will be responsible for use tax.
That is general rule - and would be used in Iowa - but there is a different sales tax law and some services taxable in Wisconsin might be not taxable in Iowa and opposite.