If the textbox is unbound, or there is not a relationship between the
table/query its bound to and the table/query your subform is based on, you
will need an event to trigger the updates in the subform. This can most
easily be accomplished with a button's OnClick event in the main form, or
using the main form's OnCurrent event, depending on your specific
configuration.
The vba code would look something like this (the braces {/} will be used to
describe the names in your specific database, and should be removed from the
code once you have entered the appropriate names):
'//This Code may paste into more than one line, if so, make sure that it
ends up on one line only
me.{SubformName}.form.recordsource = "Select {TableName}.{Vendor},
{TableName}.{Invoice}, {TableName}.{Date} From {TableName}
Where(({TableName}.{Vendor}) = '" & me.{TextboxName} & "')"
If your textbox is bound, and the field it is bound to is part of a
relationship with your subform's data source, then the method is much simpler:
In the Properties window for your subfrom, click on the "Data" tab. Select
the related fields for the Link Master Fields and the Link Child Fields.