1. 根据报错找源码，看看有没有配置
2. 看源码或者文档，或者是 issus 解决问题

const adapter = new FastifyAdapter({
        bodyLimit: 30 * 1024 * 1024,

    });

或者

import fastify = require('fastify')
import formBodyPlugin = require('./formbody')

const app = fastify()
app.register(formBodyPlugin)
app.register(formBodyPlugin, {})
app.register(formBodyPlugin, {
  bodyLimit: 1000
})

fastify/docs/Reference/Server.md at main · fastify/fastify

https://github.com/fastify/fastify-formbody

https://github.com/fastify/fastify-formbody/pull/33/files