Is there anything that links them?
Do you have an InvoiceT which then links Products and Services?

Union Query
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Time & Billing

You can combine the two queries into a single "union query," which Richard's videos have covered.  You may also consider using two invoices, which would be easier to do in Access.  According to industry standards for commerce, you are allowed to bill inventory and non-inventory goods on a single invoice.  But business practices may demand separate invoices for goods and services.  My old job was in the wholesale/retail industry which required every invoice to be from a specific order, destination, carrier, etc., and that usually meant that an invoice could only have one type of goods.

Alex Hedley: no link between products and services.

How can I link them?

You need a union query to combine all the data, as Richard and I have suggested.  For instance,

If your product table ProductsT is this:

ProductID   ProductDesc          Price
P100         Polybags, 1 Carton     $50
P101         Hangers, 1 Carton      $60

and your service table ServicesT is this:

ServiceID   ServiceDesc       Price
S200        Packaging          $10
S201        Delivery           $10

then the union query:

SELECT ProductID AS ID, ProductDesc AS ItemDesc, Price FROM ProductsT
UNION
SELECT ServiceID AS ID, ServiceDesc AS ItemDesc, Price FROM ServicesT

will yield:

ID       ItemDesc              Price
P100     Polybags, 1 Carton     $50
P101     Hangers, 1 Carton      $60
S200     Packaging              $10
S201     Delivery               $10

If you are unfamiliar with union queries and all their caveats, you need to see Richard's videos on the topic.

Most importantly, you need some way to tell which is which. In Kevin's example, he used "P" for a product and an "S" for a service item. You could add those yourself or use some other method to determine which is which, but the basic concept is the same.

Thank you so much.