There is NO special business license - and you may start servicing this and may be other similar clients.
You may expect the payer will issue 1099misc form reporting the payment to you in box 7 as non-employee compensation.
You will get this form in January of the following year and will use it fro your tax return preparation.
You actually will be treated as running your own business and will report all business income and expenses - on the schedule C -
The net income (after deductions) will be reported on the form 1040 line 12 -
If the business has net income over $400, it may be required to file Schedule SE, Self-Employment Tax
and net self-employment income is subject to 15.3% self-employment tax.
Self-employment taxes from schedule SE will go to the form 1040 line 57 -
Also - you will deduct half of self-employment taxes on the form 1040 line 27.
Generally - that all you needs tax purposes.
You may also find helpful following publication
Please verify your possible business expenses - that will help to reduce your tax liability.