PayPal recommended to use Express checkout client side integration and you can send the amount dynamically from your website to PayPal code.
Refer the following links for PayPal Express checkout client side integration:
https://developer.paypal.com/docs/integration/direct/express-checkout/integration-jsv4/client-side-REST-integration/
https://developer.paypal.com/demo/checkout/#/pattern/client
Otheriwse, please try with the below PayPal HTML button code.
<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
<!-- Identify your business so that you can collect the payments. -->
<input type="hidden" name="business" value="[email protected]"> <!-- Add your PayPal Seller/Business email address Required-->
<!-- Specify a Buy Now button. -->
<input type="hidden" name="cmd" value="_xclick">
<!-- Specify details about the item that buyers will purchase. -->
<input type="hidden" name="item_name" value=""> <!-- Add Description e.g your room type Required-->
<input type="hidden" name="amount" value=""> <!-- Dynamically add Total Amount Required-->
<input type="hidden" name="currency_code" value=""> <!-- Update to your currency -->
<input id="invoice" type="hidden" value="" name="invoice"> <!-- Add Unique invoice for each transaction -->
<input type="hidden" name="notify_url" value="www.yourwebsite.com/ipn.php"> <!-- Please add IPN URL You can use this service to automate back-office and administrative functions, including fulfilling orders, tracking customers, and providing status and other information related to transactions. -->
<input type='hidden' name='cancel_return' value='' /> <!-- Take customers to this URL when they cancel their checkout -->
<input type='hidden' name='return' value='' /> <!-- Take customers to this URL when they finish their checkout -->
<!-- Display the payment button. -->
<input type="image" name="submit" border="0" src="https://www.paypalobjects.com/en_US/i/btn/btn_buynow_LG.gif" alt="PayPal - The safer, easier way to pay online">
</form>
HTML Variables - https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/Appx_websitestandard_htmlvariables/
Buy Now button - https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/buy_now_step_1/
IPN - https://developer.paypal.com/docs/classic/ipn/gs_IPN/
IPN - https://developer.paypal.com/docs/classic/ipn/integration-guide/IPNSetup/
IPN Sample: https://github.com/paypal/ipn-code-samples