By Niket Nishant and Manya Saini

July 31 (Reuters) - As PayPal embarks on an ambitious turnaround strategy to revitalize growth after a post-pandemic slump, Wall Street analysts expressed some caution over competition from big-tech and beyond.

The concerns highlight the challenges to the profit margins of the company, which for years enjoyed the first-mover advantage in the digital payments industry but has ceded market share more recently to newer entrants.

Technology behemoths such as Apple and Alphabet's Google have taken some share in mobile payments, according to analysts.

Apple is a bigger threat. Andrew Jeffrey, analyst at brokerage William Blair, said Apple Pay is "increasingly ubiquitous". The company has also partnered with Affirm for its 'buy now, pay later' service.

"We are guarded on (PayPal's) ability to drive meaningful card present and Venmo monetization, particularly given the rise of competing contactless payments and Apple Pay," Jeffrey said.

Venmo is PayPal's peer-to-peer payments platform.

PayPal shares have gained 4.2% so far this year, trailing the benchmark S&P 500 index's nearly 14% gain.

The company on Tuesday raised its forecast for full-year adjusted profit for the second time. While executives acknowledged rising competition in a call with analysts, CEO Alex Chriss said it had not lost any market share in desktop or web-based checkout.

Its dominance could, however, be challenged by physical card issuers such as Mastercard, which is aiming to phase out the manual card entry requirement for online payments in Europe by 2030 and potentially erode the edge digital firms have enjoyed.

"While this initiative is long-dated, it reinforces the fact that competition for PayPal's core checkout button could continue to intensify," analysts Verified VCC At Cheap Price - Quickvcc BofA Global Research wrote in a note.

(Reporting by Manya Saini and Niket Nishant in Bengaluru; Editing by Krishna Chandra Eluri)