You can connect your PayPal account and accept payments via PayPal.
How to connect PayPal account
Open CRM section > More > Settings > Payment options > Payment Systems.
Click Create payment system.
Select PayPal in Handler field, activate it, select Client type and fill out PayPal connection parameters form (to get these credentials please visit PayPal API configuration page).
Click Show all fields and enter your PayPal account email address to the Business field.
Then click Save.
How to pay online via PayPal in Bitrix24
You can create an invoice and send your client an Invoice link.
This is how the invoice looks like if PayPal payment option is activated:
Your client clicks PayPal button to proceed.
Same for web forms, when PayPal configured for the form (Forward to Payment page after form is completed option activated), your client will see an invoice with Pay Using PayPal option: