Ask HN: Tell me about your painful vendor migration

Hello! I'd like to ask if you'd be willing to talk to us about painful vendor migrations that you've experienced. I've done tons of messy migration work in the past (ERPs, credit card processors, shipping/warehouse services) at large companies. I'm thinking of striking out on my own and forming a company to focus on just that: automating away messy work that normally require consultants. Can you tell share your horror stories about vendor changes that stick out in your mind as painful, or required consultants, or that you want to change but feel stuck? Here are some examples: - Shipping and logistics. For example, supporting both UPS and FedEx, changing shipping couriers, using a 3PL, changing warehouses - E-Commerce. Switching from Squarespace to Shopfiy, or from brick-and-mortar to online. Supporting both Seamless and Doordash. - Content. Wordpress to Contentful, or Squarespace to Wix. - Payments. Adding PayPal support, or moving from PayPal to Stripe. Migrating away from Vantiv, or on to Authorize. - ERP. Moving from Quickbooks to Netsuite. - HR. Moving from ADP -> Gusto. Culture Amp to Lattice. Fidelity to Vanguard for managing defined benefits. - BI tools. Adopting Looker. Or shifting from Postgres to Redshift. - File storage. Migrating from S3 to GCP. Moving your org from Google Drive to Dropbox. - Productivity. Monday to JIRA. Confluence to Notion. - Cloud infrastructure. Cloud migrations: multi-cloud deployments, or changing your containerization deployment strategy. Moving from GCP to AWS. Consolidating your domain registrations. - Communication. Gmail to Outlook. Mailgun to Sendgrid. Hipchat to Slack. What was painful? Where did you start looking for consultants to do the work? What migration made your team start looking for new jobs? Where do you feel completely stuck but it's too much work to move?