Create and manage a standard Salesforce Quote and QuoteLineItems via the REST API

Steps

1. Standard Salesforce Quotes (the Quote standard object, not CPQ) are linked to Opportunities; create a quote by POSTing to /services/data/{apiVersion}/sobjects/Quote with fields: Name, OpportunityId, Status, ExpirationDate, and Pricebook2Id.
2. Add line items by creating QuoteLineItem records: POST /services/data/{apiVersion}/sobjects/QuoteLineItem with fields QuoteId, PricebookEntryId, Quantity, and UnitPrice.
3. Retrieve a quote with its line items using a SOQL query: SELECT Id, Name, (SELECT Id, Product2Id, Quantity, UnitPrice FROM QuoteLineItems) FROM Quote WHERE Id = '{quoteId}'.
4. To sync a quote back to the opportunity (so the opportunity's amount reflects the quote), use the standard Salesforce quote-to-opportunity sync, which requires the Syncing field or an appropriate button action; programmatically, set the IsSyncing field to true on the Quote record (verify field availability in your API version).
5. Update a line item: PATCH /services/data/{apiVersion}/sobjects/QuoteLineItem/{lineItemId} with the fields to change.
6. To generate a quote PDF using a standard quote template, use the standard Quote PDF generation mechanism (via UI or the Salesforce Connect API if available for your version); direct REST-based PDF generation for standard quotes is limited.