This guide explain how to prevent start day selection and finish of days selection (check-in and check-out) on Sunday.
In the similar way you can configure system for any other weekdays.

Such configuration possible in the Booking Calendar Business Medium or higher versions.

Important. Firstly please read about the configuration of days selection in the Booking Calendar shortcode in this FAQ guide.

1) Please enable the range days selection mode with 2 mouse clicks at the WP Booking Calendar > Settings General page in "Calendar" section and define check in day for all weekdays, excluding the Sunday, as in screenshot bellow.

2) Then configure the shortcode like this:

Please try to use something like this:

[booking resource_id=1 options='{calendar months_num_in_row=1 width=100% cell_height=50px},
{select-day condition="weekday" for="1" value="1,2,3,4,5,6,8"},
{select-day condition="weekday" for="2" value="1,2,3,4,5,7,8"},
{select-day condition="weekday" for="3" value="1,2,3,4,6,7,8"},
{select-day condition="weekday" for="4" value="1,2,3,5,6,7,8"},
{select-day condition="weekday" for="5" value="1,2,4,5,6,7,8"},
{select-day condition="weekday" for="6" value="1,3,4,5,6,7,8"}']

As you can see here I defined the start day selection for each weekdays, which defined by parameter for="X"

where values of the "for" parameter are mean following: 0 - Sunday, 1 - Monday, 2 - Tuesday, 3 - Wednesday, 4 - Thursday, 5 - Friday, 6 - Saturday.

and for value parameter I defined how many days to select for specific starting weekday. You can see that there skipped specific number of days to select. It is exact number of days, when user start selection on specific weekday and can not finish selection on Sundays.

For example, if start selection on Monday, then user can not select 7 days, that is why we use this:

{select-day condition="weekday" for="1" value="1,2,3,4,5,6,8"},